Ollie Rayner's career-best of 8-46 accelerated Middlesex towards a victory over Surrey at the Kia Oval - a win which would push their London rivals deeper into the LV= County Championship Division One relegation mire.
Surrey fell to 145 all out in their first innings as off-spinner Rayner sliced through them during a remarkable afternoon session which they began looking reasonably secure at 59-1 in reply to Middlesex's first innings of 294.
By the close Surrey were 282 runs adrift as Middlesex reached 133-5 in their second innings, with Dawid Malan finishing unbeaten on 28 and not even Gary Keedy's 5-42 enough to bring Surrey back into the game.
The second day was dominated by Surrey's dramatic collapse and belonged to all-rounder Rayner.
The 27-year-old, who is very tall for a spinner at 6ft 5in, used his height well to get extra bounce from a dusty Oval surface as well as being able to push the ball through and deny Surrey's batsmen the chance to get down the pitch to him.
Initially introduced at the Pavilion End, he switched to the Vauxhall End after just two overs and, in his third over - the penultimate over of the morning session - he gave a hint of what was to come by ripping a ball past Rory Burns' forward defensive as it turned and bounced into the gloves of wicketkeeper John Simpson.
Surrey had begun the day well by picking up the last three Middlesex first innings wickets for just 14 runs, after they had resumed on 280-7.
Jade Dernbach had James Harris leg-before for 11 with the second ball of the day, and Ravi Patel was held at first slip off Stuart Meaker for one.
Neil Dexter, on 77 overnight, tried to hit out in a bid to gain a third batting point, but he was left stranded on 90 not out when last man Corey Collymore was out in bizarre fashion as he ducked a slower ball from Dernbach - only for it to loop over him and clatter into the leg stump on the full.
Surrey then lost Arun Harinath to the new ball, caught for a second-ball duck by Rayner at second slip as he pushed out at Harris, but Burns and Hashim Amla seemed to steady the innings with a partnership of 70.
The final ball of the fourth over after lunch, however, was a low full toss from slow left-arm spinner Patel which South African Test star Amla, on 26, hit straight to Rayner at mid-on.
Almost immediately, Burns turned Rayner into Sam Robson's hands at short leg to depart for 38, and the slide continued apace when Zander de Bruyn (16) top-edged a sweep at Rayner to short fine leg and Steven Davies (one) also fell to a sharp short leg catch by Robson.
It was 117-6 when Vikram Solanki, much to his disgust, skipped down the pitch on 24 to drive Rayner to short mid-wicket where Dexter pulled off a fine diving catch to his left, and Meaker was out in similar fashion for three.
Tim Linley was caught off bat and pad at backward short leg for two, Gareth Batty was leg-before playing no stroke for 13, after clubbing Rayner for a couple of defiant fours, and the end came when Dernbach swung a simple catch to Harris on the deep mid-wicket boundary.
Surrey had lost nine wickets inside 33 overs, and not even five wickets for Keedy, their left-arm spinner, after tea could prevent Middlesex from moving into a seemingly impregnable position by stumps.
Keedy had Robson, Dexter and Gareth Berg caught by Solanki in the gully - for 18, 14 and 15 respectively, while Rogers went for 32 from 39 balls and Simpson for 12.
Malan, however, kept up the attacking approach while Harris came in as a nightwatchman ahead of Rayner and migraine victim Joe Denly to keep him company until the close.